With what is known as the room-and-pillar method, first a main stretch is excavated (“development”), the width of which corresponds essentially to the width of the roadheading machine. This is followed by mining outwards laterally from the main stretch to form chambers (“retreat mining”). In the retreat mining phase, the supporting of the cavity areas by installed elements is done without. Instead, the material is mined out of chambers, and pillars of rock or coal are left standing respectively in order to support the roof. Taking account of the pillars which are left standing in each case, the conveying means provided for conveying away the mined material must overcome frequent changes of direction and tight curve radii. In the roadway/stretch it is possible, at a point located further back, for a conventional conveying means to be arranged, for example in the form of stationary conveying belts installed subsequently. In order to allow transport from the actual point of excavation and working to a stationary conveying means even with tight curves of this type, it has already been proposed that what are referred to as “shuttle” vehicles are used, which transport the material from the roadheading machine to the stationary conveying device arranged further back in the roadway.
As an alternative to “shuttle” vehicles, the principle is also known of guiding the conveyor belt as far as directly behind the excavating equipment, and continually moving it forwards in step with the development. For this purpose, the conveying device is in most cases formed of at least two different types of conveying elements, namely of a plurality of stationary conveyor elements which can be coupled to one another in order to form one stationary conveying device, and a plurality of movable conveying elements. The movable conveying elements can in this situation be drawn along immediately behind the excavating equipment, and form a continuously extendible conveying section. The gap which is thereby formed between the conveying elements being drawn behind and the stationary elements can be bridged by the introduction of additional conveying elements. In order to avoid interruptions in the operation of conveying material away, conveyor belt stores are known, which store the conveyor belt in a multiple folded compressed state, and from which a reserve length of conveyor belt can be drawn out.
Due to the change of direction of the conveying stretch, the endless conveyor belt, in particular with the room-and-pillar method, must be deflected between a first stretch section and a second stretch section running transversely to the first stretch section. The deflection can, as shown, for example, in DE 3347855 C2, take place without the ejection of material. As a rule, however, a material handover takes place between the first stretch section and the second stretch section running transversely to the first stretch section. The material handover can take place in this situation at an angle station with integrated belt deflection, as is described in U.S. Pat. No. 3,016,127 or WO 93/06028, wherein the material handover takes place on the same conveyor belt. The material handover can also take place onto a separate conveyor belt, which runs in the stretch section running transversely. A deflection device is only required in such a case if, as is frequently provided for with the room-and-pillar method, in this case transversely running main stretch is arranged relative to the belt store of the continuously developing belt conveyor.
Deflection devices comprise at least one first turning device and a second turning device for the conveyor belt. The first and second turning devices comprise, at an angle station (see, for example, U.S. Pat. No. 3,016,127), in each case a plurality of horizontal deflection rollers for the conveyor belt, wherein in each case at least one deflection roller encloses an angle of 45° with the direction of movement of the belt.
A disadvantage with conventional deflection devices is that an exact and elaborate method of guiding the conveyor belt is required. As well as this, conventional deflection devices are not flexible in use, since they are mostly designed for a predetermined deflection angle of, for example, 90°. Minor deviations from the predetermined deflection angle lead to imprecise belt guidance and to the risk of frequent operational interruptions.